Fire-resistant hydraulic fluid

ABSTRACT

Fire-resistant hydraulic fluids having improved low temperature characteristics, e.g., viscosity, pour point, and cloud point, consist mainly of a mixture of a synthetic hydrocarbon, a dialkyl carboxylate ester and an orthosilicate.

United States Patent [1 1 Burrous Feb. 19, 1974 FIRE-RESISTANT HYDRAULICFLUID [75] Inventor: Merwyn L. Burrous, El Cerrito,

Calif.

[22] Filed: Nov. 5, 1971 [21] Appl. No.: 196,209

[52] US. Cl. 252/78, 252/49.6 [51] Int. Cl C09k 3/02 [58] Field ofSearch 252/78, 75, 49.6, 73

[56] References Cited UNITED STATES PATENTS 2,550,760 5/1951 Bishop252/79 2,691,633 10/1954 Benoit 252/49.6 2,960,474 11/1960 Furby et al.252/78 3,296,138 1/1967 Cupper et al... 252/78 X 3,478,113 11/1969 Brayet a1. 252/73 X 3,513,097 5/1970 Langenfeld 252/78 3,538,001 11/1970Gothel et al. 252/78 X 3,637,507 1/1972 Gentit 252/78 2,509,620 5/1950Watson et a1 252/78 2,746,926 5/1956 Barry 252/78 3,074,889 1/1963252/78 3,657,128 4/1972 Street 252/78 X OTHER PUBLICATIONS SyntheticLubricant Fluids from Branched Chain Diesters, Industrial EngineeringChemistry, Vol. 39 (1947) pp. 484, 489.

Primary Examiner-Richard D. Lovering Attorney, Agent, or FirmJ. A.Buchanan, Jr.

[5 7 ABSTRACT Fire-resistant hydraulic fluids having improved lowtemperature characteristics, e.g., viscosity, pour point, and cloudpoint, consist mainly of a mixture of a synthetic hydrocarbon, a dialkylcarboxylate ester and an orthosilicate.

7 Claims, No Drawings FIRE-RESISTANT HYDRAULIC FLUID BACKGROUND OF THEINVENTION 1. Field of the Invention A hydraulic fluid should befire-resistant; it should not adversely affect the materials ofconstruction of the system in which it is used; it must possess adequatelubricity and mechanical stability; it must be chemically stable; itmust possess good low temperature properties such as viscosity, pourpoint and cloud point; and, finally, it must be low foaming. Thesecharacteristics have been summarized in specification MIL-I-I-83282.

2. Description of the Prior Art Aryl and alkyl phosphates are widelyused in fireresistant hydraulic fluids to provide both flame resistanceand lubricity. Petroleum-base oils, though good lubricants andeconomically desirable, are not often used in high proportions infire-resistant hydraulic fluids because of their flammability.Chlorinated hydrocarbons are often used as good flame retardants forpetroleum-base oils. A typical fire-resistant hydraulic fluid would be aphosphate ester, a chlorinated hydrocarbon or a mixture of these with orwithout a minor amount of mineral oil.

SUMMARY OF THE INVENTION We have discovered that a fire-resistantfunctional fluid can be prepared from a synthetic hydrocarbon oil, 20-30percent by weight of an ester of a dicarboxylic acid and -1 5 percent ofan alkyl silicate, with small percentages of other functional additives.Such functional additives include antiwear agents, such as tricresylphosphate, antioxidants such as dialkyl paracresol, hydrolysissuppressants such as cycloaliphatic epoxides, and antifoamants.

The synthetic hydrocarbon oil of the present invention comprisessubstantially a dialkyl aromatic hydrocarbon oil having a viscosity offrom 8,500 to 10,000 cs at 40F., 25-35 cs at 100F., and 4-8 cs at 210F.The preferred ester of a dicarboxylic acid is a dialkyl adipate ester ofa C C alcohol. This fluid is hydrolytically stable, has excellent lowtemperature properties such as viscosity, pour point and cloud point,and has a high flash point, fire point, and autogenous ignitiontemperature.

DESCRIPTION OF THE INVENTION The hydrocarbon oils suitable for purposesof the present invention comprises hydrocarbons and mixtures ofhydrocarbons which are alkyl, alkenyl, aryl and aralkyl hydrocarbons.Individual hydrocarbons will contain from about 8 to about 50 carbonatoms and be chosen from the classes of aromatic, alkyl aromatic,alkane, alkene, paraffinic and naphthenic molecules. The hydrocarbon oilis present in the hydraulic fluid composition to the extent of 30-80percent by weight of the total composition. An important characteristicof the hydrocarbon oil is its viscosity, especially at low temperatures.The viscosity should range from 8,000 to 10,000 cs at 40F., to 40 cs at100F., and 2-10 cs at 212F. A preferred oil is substantially a dialkylaromatic hydrocarbon such as di(tridecyl)benzene,tridecyl-(tetradecyl)benzne, di(tetradecyl)benzene, or mixtures of same.The hydrocarbon oil may be a dewaxed mineral oil, or preferably asynthetic hydrocarbon oil. A synthetic hydrocarbon oil is preferred overa mineral oil because of its lower pour point. The most stable mineraloils are parafi'mic in nature and characterized by their high pourpoints. The pour point is the lowest temperature at which the oil isobserved to flow when cooled and examined under prescribed conditions,ASTM D 97-66. However, in choosing a synthetic hydrocarbon oil for itspour point, the viscosity of the oil, its flammability, and otherproperties, must be balanced by the discovery of additional componentsto form the base fluid meeting the severe specifications of the presentinvention.

The second important component of the hydraulic fluid is an ester of a C-C dicarboxylic acid, i.e., a dialkyl carboxylate. Such acids includeoxalic, succinic, malonic, glutaric, adipic, pimelic, suberic, azeleicacid, and substituted acids of the same names. The alcoholic portion ofthe ester is derived from a C C, aliphatic alcohol such as methyl,ethyl, propyl, butyl, amyl, hexyl, hectyl, octyl, nonyl, decyl, andundecyl alcohol. These terms include all geometrical isomers, e.g., theterm butyl alcohol includes isobutyl alcohol. For best over-allperformance in low temperature viscosity, rubber swell, cost, stabilityand flash point, a dialkyl ester of adipic acid is preferred. The esterwill usually be present in 10-40 percent by weight and preferably 15-35percent by weight.

The third important component of the hydraulic fluid is an alkylsilicate ester of the general formulae SIOR O R R R x R wherein R (wherei l-8) is an alkyl group of from 3-12 carbon atoms and preferably from6-10 carbon atoms, and x has the value of 0 or 1. Examples of thealkylsilicates include isopropyl orthosilicate, butyl orthosilicate,hexyl orthosilicate, 2-ethyl hexyl orthosilicate, 2-ethylbutoxydisiloxane, 3-propyl heptyl orthosilicate, and Z-methyl hexylorthosilicate. The alkylsilicate esters will usually be present in 2-25percent by weight and preferably 5-20 percent by weight.

The hydrocarbon oil, dicarboxylate ester and alkylsilicate ester formthe fire-resistant base stock of the present hydraulic fluid. Specificadditives are combined with this base stock to impart particular properties. For example, antiwear agents, antioxidants, hydrolysissuppressants, rust inhibitors, antifoamants, and additional viscosityindex improvers may be added in small percentages. Specifically, atriaryl phosphate, and preferably tricresyl phosphate is present in theamount of 0.5-3 percent by weight, as is a dialkyl paracresol, such asdipropyl paracresol, dibutyl paracresol, or dihexyl paracresol. A verysmall amount (0.05-0.5 weight percent) of a diepoxide as described in USapplication Ser. No. 865,471, filed Oct. 10, 1969 and now abandoned, isusually present as a hydrolysis suppressant. Usually an antifoamant willbe present in percentages below 0.01 percent by weight.

The hydrolytic stability of the composition is excellent. It undergoeslittle change in acid number, viscosity, or flash point when subjectedto 275F. for one week even in the presence of added water.

The following are typical examples of base fluid formulations which arein accord with this invention. They are given by way of illustration andnot by limitation. The ingredients are known and commercially availablechemicals. The fluids are prepared by simply mixing together thecomponents of Table I with small amounts (0.5 percent or less) ofspecific additives discussed hereinbefore, such as antifoamant andhydrolysis suppressant, at l40l 50F.

The properties of the fire-resistant hydraulic fluid of Table l aresummarized in Table 11. This fluid meets or exceeds MlL-H-83282specifications in these categories; oxidation-corrosion inhibition, lowtemperature stability, lack of rubber swelling, low foaming tendency,water content below 100 ppm, lack of solid contamination, lubricity,resistance to flame propagation, and compatibility with other fluidsTABLE II Property MlL-H-83282 Fluid Viscosity, cs

100F 16.5 minimum 17.0

210F 3.5 minimum 3.74

Flash point, "F ASTM D 92 400 minimum 420 Fire Point, F ASTM D 92, 475minimum 475 Acid No., mg KOH/g ASTM D 974 0.10 maximum 0.01

Pour Point, F 65 maximum 80 Lubricity, 4-Ball Wear Test 40 kg, Scardiameter, mm 0.65 maximum 0.52, 0.53

This specification describes a hydraulic fluid which is fire-resistantand has a synthetic hydrocarbon base. Hydraulic Fluid B of Table I.

In addition, this fluid has been subjected to additional tests which arenot within the scope of MIL-H-83282 specifications. These results aresummarized in Table 111.

Shear Stability TABLE Ill-Continued Property Fluid Percent viscosityloss after 2 hours in sonic oscillator Oxidation Hours to absorb 1 literof 0 ml of fluid at 340F 14.4

Hydrolytic Stability Percent change in viscosity 2.0 Final acid number0.10

Metal weight change, mg/em Copper 0.02 Magnesium +0.06 Aluminum +0.00Iron +0.08 Cadmium -0.01

Hydraulic Fluid 8 of Table 1. In this test, ml offluid, 0.15 percent byweight of H 0 and 5 metal specimens are sealed in a 250 ml jar underair. The jar is rotated end over end at 5 rpm for 1 week at 275F.

The fire resistance of the fluids of the present invention isdemonstrated by the flash point and fire point of Table II and by thefollowing test comparisons with a petroleum-base hydraulic fluid meetingSpecification MIL-H-5606B (see Table IV).

TABLE IV Fluid B in Table l M1L-H-5606B Hydraulic Fluid,

Petroleum Base number of passes Flame Propagation No propagation afterPropagation after 36 MlL-H-83282, Sec. 2 hours seconds 4.4.3.1.1

High Ignites with lgnites when any portion Temperature-High PressureSpray Ignition, Fed. Std. 791-6052 difficulty. Does not of flame touchesany continue to burn portion of stream. after source of Continues toburn ignition is removed. vigorously when ignition source is removed.

As will be evident to those skilled in the art, numerous modificationsand variations of the invention illustrated above may be made withoutdeparting from the spirit of the invention, or the scope of thefollowing claims.

I claim:

1. A fire-resistant hydraulic fluid comprising a base stock consistingessentially of;

30-80 percent by weight of a hydrocarbon oil having a maximum viscosityof 10,000 cs at 40F. and a minimum viscosity of 4 cs at 210F.,

15-35 percent by weight of a dialkyl carboxylate ester of a C -C alkanoland a C -C dicarboxylic acid, and

5-20 percent by weight of an alkyl silicate ester of the generalformulae:

0 0 O O R 0SiOR or R OSi-O Si-O- SiOR a a Ra x R:

wherein the R, i being an integer of from 1-8, are alkyl groups of from3 to 12 carbon atoms and x has the value of or I.

2. The fire-resistant hydraulic fluid of claim 1, in which thehydrocarbon oil is a dialkyl aromatic hydrocarbon oil, wherein the alkylcontains 12-14 carbon atoms.

3. The fire-resistant hydraulic fluid of claim 1, in which the alkyl ofthe alkyl silicate contains from 6-! 0 carbon atoms.

4. The fire-resistant hydraulic fluid of claim 1, in which thecarboxylic acid is of the form HOOC(CH drolysis suppressant.

2. The fire-resistant hydraulic fluid of claim 1, in which thehydrocarbon oil is a dialkyl aromatic hydrocarbon oil, wherein the alkylcontains 12-14 carbon atoms.
 3. The fire-resistant hydraulic fluid ofclaim 1, in which the alkyl of the alkyl silicate contains from 6-10carbon atoms.
 4. The fire-resistant hydraulic fluid of claim 1, in whichthe carboxylic acid is of the form HOOC(CH2)xCOOH, where x 2 to
 10. 5.The fire-resistant hydraulic fluid of claim 1, in which the dialkylcarboxylate ester is diisooctyl adipate.
 6. The fire-resistant hydraulicfluid of claim 4, in which the alkyl silicate is 2-ethylhexylorthosilicate.
 7. The fire-resistant hydraulic fluid of claim 1,additionally containing 1-3 percent by weight of tricresyl phosphate,0.5-2 percent by weight of dialkyl paracresol, and 0.05-0.5 percent byweight of a diepoxide hydrolysis suppressant.